The passage of the Family Smoking Prevention and Tobacco Control Act in June 2009 empowers the Food and Drug Administration to regulate tobacco products. In the FSPTC, there is significant focus on tobacco products and its evaluation. One critical component of this product evaluation process is human clinical trials. These trials will inform the regulatory agency about the uptake of the product, how the product is used, the extent of toxicant exposure and possible health risk associated with this pattern of use. To date, no study has examined the best experimental methods to provide the information that is necessary to make a sound scientifically-based decision about a tobacco product (e.g., modified risk tobacco products) or any regulations imposed on tobacco products (e.g., performance standards) that assures no public harm will result based on this decision. The goals of this research project are to test a clinical trial method for assessing tobacco products and also address some methodological gaps so that guidance can be provided to the FDA and other international regulatory agencies on the best measures and methods for the evaluation of tobacco products. This trial is a between-subject, parallel-arm design in which subjects are randomized to one of the five experimental conditions, with different instructional sets, for a period of 12-weeks. The product chosen for testing is an oral tobacco product. Camel Snus. The instructional sets include: complete substitution vs. partial substitution for cigarettes by ad libitum use vs. specific instruction for snus use. A control group of continuing smokers will also be included in the design. The primary outcome measures include biomarkers of toxicant exposure and effect and subjective responses to the product. The overall goal for this P01 is to assimilate the results from this Project with the results from the other P01 Projects to determine consistency of findings across studies, predicitive validity of measures, and to determine if the proposed